Data compressing apparatus and a data decompressing apparatus, a data compressing method and a data decompressing method, and a data compressing or decompressing dictionary creating apparatus and a computer readable recording medium storing a data compressing program or a data decompressing program

Abstract

A data compressing technique and a data decompressing technique provide a compressing dictionary storing unit for storing a compressing dictionary usable when data to be compressed is compressed, a compressing dictionary use or non-use deciding unit for deciding whether the compressing dictionary is to be used or not when the data to be compressed is compressed, and a coding unit for coding the data to be compressed on the basis of the compressing dictionary when the compressing dictionary use or non-use deciding unit decides the compressing dictionary is to be used, whereas not coding but outputting the data to be compressed when the compressing dictionary use or non-use deciding unit decides the compressing dictionary is not to be used, thereby stably achieving a preferable compression ratio for a small quantity of data such as text data in a text file.

What is claimed is:  
     
       1. A data compressing apparatus for coding inputted data to be compressed, comprising: 
       a compressing dictionary storing unit for storing a compressing dictionary usable to compress said inputted data;  
       a compressing dictionary use or non-use deciding unit for deciding whether said compressing dictionary is to be used or not when said inputted data is considered for coding; and  
       a coding unit for coding said inputted data on the basis of said compressing dictionary when said compressing dictionary use or non-use deciding unit decides said compressing dictionary is to be used and outputting the coded data, and outputting the same inputted data without coding when said compressing dictionary use or non-use deciding unit decides said compressing dictionary is not to be used.  
     
     
       2. The data compressing apparatus according to  claim 1  further comprising: 
       a compressed data dividing unit for dividing said data to be compressed into predetermined character data groups;  
       wherein said coding unit codes said data to be compressed by said character data group obtained by said compressed data dividing unit.  
     
     
       3. The data compressing apparatus according to  claim 2 , wherein if said data to be compressed is document-form data, said compressed data dividing unit comprises: 
       a word dictionary storing unit for storing a word dictionary in which desired words are registered as said character data groups occurring in said document-form data; and  
       a word dividing unit for dividing said data to be compressed into words on the basis of said words registered in said word dictionary in said word dictionary storing unit.  
     
     
       4. The data compressing apparatus according to  claim 2 , wherein if said data to be compressed is document-form data, said compressed data dividing unit comprises: 
       a word category dictionary storing unit for storing a word category dictionary in which a desired word as each of said character data groups occurring in said document-form data and category information on said word are registered;  
       a word dividing unit for dividing said data to be compressed into words on the basis of said words registered in said word category dictionary in said word category dictionary storing unit; and  
       a category information adding unit for adding said category information corresponding to each of said words obtained by said word dividing unit on the basis of said category information registered in said word category dictionary.  
     
     
       5. The data compressing apparatus according to  claim 1  further comprising: 
       a characteristic extracting unit for extracting character data inherent to said data to be compressed as characteristic data of said data to be compressed; and  
       a compressing inherent dictionary creating unit for assigning a predetermined code to each of said characteristic data extracted by said characteristic extracting unit to create a compressing inherent dictionary inherent to said data to be compressed;  
       wherein said coding unit codes said data to be compressed on the basis of said compressing inherent dictionary created by said compressing inherent dictionary creating unit and said compressing dictionary in said compressing dictionary storing unit.  
     
     
       6. The data compressing apparatus according to  claim 5  further comprising: 
       an inherent dictionary information outputting unit for outputting information on said compressing inherent dictionary to a decompressing side for said data to be compressed.  
     
     
       7. The data compressing apparatus according to  claim 1  further comprising: 
       a compressing dictionary updating unit for updating said compressing dictionary on the basis of data to be compressed having been coded by code in said coding unit;  
       wherein said coding unit codes said data to be compressed on the basis of said compressing dictionary updated by said compressing dictionary updating unit.  
     
     
       8. The data compressing apparatus according to  claim 1 , wherein said compressing dictionary use or non-use deciding unit decides whether said compressing dictionary is to be used or not on the basis of data contents type information representing a type of data contents of said data to be compressed. 
     
     
       9. The data compressing apparatus according to  claim 1 , wherein said compressing dictionary use or non-use deciding unit decides whether said compressing dictionary is to be used or not according to whether specific character data occurs in said data to be compressed or not. 
     
     
       10. The data compressing apparatus according to  claim 1 , wherein said compressing dictionary use or non-use deciding unit decides whether said compressing dictionary is to be used or not according to occurrence frequency of specific character data in said data to be compressed. 
     
     
       11. The data compressing apparatus according to  claim 1 , wherein said compressing dictionary use or non-use deciding unit decides whether said compressing dictionary is to be used or not according to a quantity of compressed data having been coded by said coding unit. 
     
     
       12. The data compressing apparatus according to  claim 1  further comprising: 
       a dictionary use or non-use information outputting unit for outputting information on use or non-use of said compressing dictionary decided by said compressing dictionary use or non-use deciding unit to a decompressing side for said data to be compressed.  
     
     
       13. A data compressing apparatus for coding inputted data to be compressed, comprising: 
       a compressing dictionary storing unit for storing plural different kinds of compressing dictionaries usable to compress inputted file data to be compressed;  
       a compressing dictionary selecting unit for selecting a compressing dictionary to be used among said plural different kinds of compressing dictionaries on the basis of an extension of a file name of the inputted file data; and  
       a coding unit for coding said inputted file data on the basis of said compressing dictionary selected by said compressing dictionary selecting unit.  
     
     
       14. The data compressing apparatus according to  claim 13  further comprising: 
       a compressed data dividing unit for dividing said data to be compressed into predetermined character data groups;  
       wherein said coding unit codes said data to be compressed by said character data group obtained by said compressed data dividing unit on the basis of said compressing dictionary selected by said compressing dictionary selecting unit.  
     
     
       15. The data compressing apparatus according to  claim 14 , wherein if said data to be compressed is document-form data, said compressed data dividing unit comprises: 
       a word dictionary storing unit for storing a word dictionary in which desired words are registered as said character data groups occurring in said document-form data; and  
       a word dividing unit for dividing said data to be compressed into words on the basis of said words registered in said word dictionary in said word dictionary storing unit.  
     
     
       16. The data compressing apparatus according to  claim 14 , wherein if said data to be compressed is document-form data, said compressed data dividing unit comprises: 
       a word category dictionary storing unit for storing a word category dictionary in which a desired word as each of said character data groups occurring in said document-form data and category information on said word are registered;  
       a word dividing unit for dividing said data to be compressed into words on the basis of said words registered in said word category dictionary in said word category dictionary storing unit; and  
       a category information adding unit for adding said category information corresponding to each of said words obtained by said word dividing unit on the basis of said category information registered in said word category dictionary.  
     
     
       17. The data compressing apparatus according to  claim 13  further comprising: 
       a characteristic extracting unit for extracting character data inherent to said data to be compressed as characteristic data of said data to be compressed; and  
       a compressing inherent dictionary creating unit for assigning a predetermined code to each of said characteristic data extracted by said characteristic extracting unit to create a compressing inherent dictionary inherent to said data to be compressed;  
       wherein said coding unit codes said data to be compressed on the basis of said compressing inherent dictionary created by said compressing inherent dictionary creating unit and said compressing dictionary selected by said compressing dictionary selecting unit.  
     
     
       18. The data compressing apparatus according to  claim 17  further comprising: 
       an inherent dictionary information outputting unit for outputting information on said compressing inherent dictionary to a decompressing side for said data to be compressed.  
     
     
       19. The data compressing apparatus according to  claim 13  further comprising: 
       a compressing dictionary updating unit for updating said compressing dictionary on the basis of data to be compressed having been coded by code in said coding unit;  
       wherein said coding unit codes said data to be compressed on the basis of said compressing dictionary updated by said compressing dictionary updating unit.  
     
     
       20. The data compressing apparatus according to  claim 13  further comprising: 
       a selected dictionary information outputting unit for outputting selected dictionary information on said compressing dictionary selected by said compressing dictionary selecting unit to a decompressing side for said data to be compressed.  
     
     
       21. A data compressing apparatus for coding inputted data to be compressed, comprising: 
       a compressing dictionary storing unit for storing plural different kinds of compressing dictionaries usable to compress said inputted data;  
       a compressing dictionary selecting unit for selecting a compressing dictionary including high-ranked character data of high occurrence frequency in said inputted data among said plural different kinds of compressing dictionaries; and  
       a coding unit for coding said inputted data on the basis of said compressing dictionary selected by said compressing dictionary selecting unit.  
     
     
       22. The data compressing apparatus according to  claim 21  further comprising: 
       a compressed data dividing unit for dividing said data to be compressed into predetermined character data groups;  
       wherein said coding unit codes said data to be compressed by said character data group obtained by said compressed data dividing unit on the basis of said compressing dictionary selected by said compressing dictionary selecting unit.  
     
     
       23. The data compressing apparatus according to  claim 22 , wherein if said data to be compressed is document-form data, said compressed data dividing unit comprises: 
       a word dictionary storing unit for storing a word dictionary in which desired words as said character data groups occurring in said document-form data are registered; and  
       a word dividing unit for dividing said data to be compressed into words on the basis of said words registered in said word dictionary in said word dictionary storing unit.  
     
     
       24. The data compressing apparatus according to  claim 22 , wherein if said data to be compressed is document-form data, said compressed data dividing unit comprises: 
       a word category dictionary storing unit for storing a word category dictionary in which a desired word as each of said character data groups occurring in said document-form data and category information on said word are registered;  
       a word dividing unit for dividing said data to be compressed into words on the basis of said words registered in said word category dictionary in said word category dictionary storing unit; and  
       a category information adding unit for adding said category information corresponding to each of said words obtained by said word dividing unit on the basis of said category information registered in said word category dictionary.  
     
     
       25. The data compressing apparatus according to  claim 21  further comprising: 
       a characteristic extracting unit for extracting character data inherent to said data to be compressed as characteristic data of said data to be compressed; and  
       a compressing inherent dictionary creating unit for assigning a predetermined code to each of said characteristic data extracted by said characteristic extracting unit to create a compressing inherent dictionary inherent to said data to be compressed;  
       wherein said coding unit codes said data to be compressed on the basis of said compressing inherent dictionary created by said compressing inherent dictionary creating unit and said compressing dictionary selected by said compressing dictionary selecting unit.  
     
     
       26. The data compressing apparatus according to  claim 25  further comprising: 
       an inherent dictionary information outputting unit for outputting information on said compressing inherent dictionary to a decompressing side for said data to be compressed.  
     
     
       27. The data compressing apparatus according to  claim 21  further comprising: 
       a compressing dictionary updating unit for updating said compressing dictionary on the basis of data to be compressed having been coded by code in said coding unit;  
       wherein said coding unit codes said data to be compressed on the basis of said compressing dictionary updated by said compressing dictionary updating unit.  
     
     
       28. The data compressing apparatus according to  claim 21  further comprising: 
       a selected dictionary information outputting unit for outputting selected dictionary information on said compressing dictionary selected by said compressing dictionary selecting unit to a decompressing side for said data to be compressed.  
     
     
       29. A data compressing apparatus for coding inputted data to be compressed, comprising: 
       a compressing dictionary storing unit for storing plural different kinds of compressing dictionaries usable to compress said inputted data;  
       a coding unit for coding said inputted data using any one of said plural different kinds of compressing dictionaries and outputting quantity information on a quantity of the coded data;  
       a determining unit for determining whether the quantity of the coded data is smaller than an original quantity before the coding based on the quantity information from said coding unit; and  
       a compressing dictionary selecting unit for selecting a compressing dictionary to be used among said plural different kinds of compressing dictionaries according to the determination of said determining unit.  
     
     
       30. The data compressing apparatus according to  claim 29  further comprising: 
       a compressed data dividing unit for dividing said data to be compressed into predetermined character data groups;  
       wherein said coding unit codes said data to be compressed by said character data group obtained by said compressed data dividing unit on the basis of said compressing dictionary selected by said compressing dictionary selecting unit.  
     
     
       31. The data compressing apparatus according to  claim 30 , wherein if said data to be compressed is document-form data, said compressed data dividing unit comprises: 
       a word dictionary storing unit for storing a word dictionary in which desired words as said character data groups occurring in said document-form data are registered; and  
       a word dividing unit for dividing said data to be compressed into words on the basis of said words registered in said word dictionary in said word dictionary storing unit.  
     
     
       32. The data compressing apparatus according to  claim 30 , wherein if said data to be compressed is document-form data, said compressed data dividing unit comprises: 
       a word category dictionary storing unit for storing a word category dictionary in which a desired word as each of said character data groups occurring in said document-form data and category information on said word are registered;  
       a word dividing unit for dividing said data to be compressed into words on the basis of said words registered in said word category dictionary in said word category dictionary storing unit; and  
       a category information adding unit for adding said category information corresponding to each of said words obtained by said word dividing unit on the basis of said category information registered in said word category dictionary.  
     
     
       33. The data compressing apparatus according to  claim 29  further comprising: 
       a characteristic extracting unit for extracting character data inherent to said data to be compressed as characteristic data of said data to be compressed; and  
       a compressing inherent dictionary creating unit for assigning a predetermined code to each of said characteristic data extracted by said characteristic extracting unit to create a compressing inherent dictionary inherent to said data to be compressed;  
       wherein said coding unit codes said data to be compressed on the basis of said compressing inherent dictionary created by said compressing inherent dictionary creating unit and said compressing dictionary selected by said compressing dictionary selecting unit.  
     
     
       34. The data compressing apparatus according to  claim 33  further comprising: 
       an inherent dictionary information outputting unit for outputting information on said compressing inherent dictionary to a decompressing side for said data to be compressed.  
     
     
       35. The data compressing apparatus according to  claim 29  further comprising: 
       a compressing dictionary updating unit for updating said compressing dictionary on the basis of data to be compressed having been coded by code in said coding unit;  
       wherein said coding unit codes said data to be compressed on the basis of said compressing dictionary updated by said compressing dictionary updating unit.  
     
     
       36. The data compressing apparatus according to  claim 29  further comprising: 
       a selected dictionary information outputting unit for outputting selected dictionary information on said compressing dictionary selected by said compressing dictionary selecting unit to a decompressing side for said data to be compressed.  
     
     
       37. A data decompressing apparatus for decoding inputted data to be decompressed, comprising: 
       a decompressing dictionary storing unit for storing a decompressing dictionary usable to decompress said inputted data;  
       decompressing dictionary use or non-use deciding unit for deciding whether said decompressing dictionary is to be used or not when said inputted data is considered for decoding; and  
       a decoding unit for decoding said inputted data on the basis of said decompressing dictionary when said decompressing dictionary use or non-use deciding unit decides said decompressing dictionary is to be used and outputting the decoded data, and outputting the same inputted data without decoding when said decompressing dictionary use or non-use deciding unit decides said decompressing dictionary is not to be used.  
     
     
       38. The data decompressing apparatus according to  claim 37 , wherein said decoding unit decodes said compressed data by predetermined character data group on the basis of said decompressing dictionary. 
     
     
       39. The data decompressing apparatus according to  claim 38 , wherein 
       if original data of said compressed data before compression is document-form data, said character data group is a desired word in said document-form data.  
     
     
       40. The data decompressing apparatus according to  claim 39 , wherein said decoding unit decodes said compressed data on the basis of category information on said word. 
     
     
       41. The data decompressing apparatus according to  claim 37  further comprising: 
       a decompressing inherent dictionary storing unit for storing a dictionary having character data inherent to data to be compressed that is said compressed data before compressed as characteristic data of said compressed data, in which a predetermined code is assigned to each of said characteristic data as decompressing dictionary;  
       wherein said decoding unit decodes said compressed data on the basis of said decompressing inherent dictionary in said decompressing inherent dictionary storing unit and said decompressing dictionary in said decompressing dictionary storing unit.  
     
     
       42. The data decompressing apparatus according to  claim 41 , wherein said decompressing inherent dictionary storing unit receives information on a compressing inherent dictionary created by extracting character data inherent to said data to be compressed as characteristic data of said data to be compressed and assigning a predetermined code to each of said characteristic data from a compressing side having generated said compressed data to store said decompressing inherent dictionary. 
     
     
       43. The data decompressing apparatus according to  claim 37  further comprising: 
       a decompressing dictionary updating unit for updating said decompressing dictionary on the basis of a result of decoding by said decoding unit;  
       wherein said decoding unit decodes said compressed data on the basis of said decompressing dictionary updated by said decompressing dictionary updating unit.  
     
     
       44. The data decompressing apparatus according to  claim 37 , wherein said decompressing dictionary use or non-use deciding unit decides whether said decompressing dictionary is to be used or not according to information on use or non-use of a compressing dictionary received from a compressing side having generated said compressed data. 
     
     
       45. A data decompressing apparatus for decoding compressed data to be decompressed, comprising: 
       a decompressing dictionary storing unit for storing plural different kinds of decompressing dictionaries usable to decompress compressed file data;  
       a decompressing dictionary selecting unit for receiving selected dictionary information on a compressing dictionary selected on the basis of an extension of a file name of the file data from a compressing side having generated said compressed file data to select a decompressing dictionary to be used among said plural different kinds of decompressing dictionaries on the basis of said received selected dictionary information; and  
       a decoding unit for decoding said compressed file data on the basis of said decompressing dictionary selected by said decompressing dictionary selecting unit.  
     
     
       46. The data decompressing apparatus according to  claim 45 , wherein said decoding unit decodes said compressed data by predetermined character data group on the basis of said decompressing dictionary selected by said decompressing dictionary selecting unit. 
     
     
       47. The data decompressing apparatus according to  claim 46 , wherein if data to be compressed that is said compressed data before compressed is document-form data, said character data group is a desired word in said document-form data. 
     
     
       48. The data decompressing apparatus according to  claim 47 , wherein said decoding unit decodes said compressed data on the basis of category information on said word. 
     
     
       49. The data decompressing apparatus according to  claim 45  further comprising: 
       a decompressing inherent dictionary storing unit for storing a dictionary having character data inherent to data to be compressed that is said compressed data before compressed as characteristic data of said compressed data, in which a predetermined code is assigned to each of said characteristic data as decompressing dictionary;  
       wherein said decoding unit decodes said compressed data on the basis of said decompressing inherent dictionary in said decompressing inherent dictionary storing unit and said decompressing dictionary selected by said decompressing dictionary selecting unit.  
     
     
       50. The data decompressing apparatus according to  claim 49 , wherein said decompressing inherent dictionary storing unit receives information on a compressing inherent dictionary created by extracting character data inherent to said data to be compressed as characteristic data of said data to be compressed and assigning a predetermined code to each of said characteristic data from a compressing side having generated said compressed data to store said decompressing inherent dictionary. 
     
     
       51. The data decompressing apparatus according to  claim 45  further comprising: 
       a decompressing dictionary updating unit for updating said decompressing dictionary on the basis of a result of decoding by said decoding unit;  
       wherein said decoding unit decodes said compressed data on the basis of said decompressing dictionary updated by said decompressing dictionary updating unit.  
     
     
       52. A data decompressing apparatus for decoding compressed data to be decompressed, comprising: 
       a decompressing dictionary storing unit for storing plural different kinds of decompressing dictionaries usable to decompress said compressed data;  
       a decompressing dictionary selecting unit for receiving selected dictionary information on a compressing dictionary selected as a compressing dictionary including high-ranked character data of high occurrence frequency in data to be compressed from a compressing side having generated said compressed data to select a decompressing dictionary to be used among said plural different kinds of decompressing dictionaries on the basis of said received selected dictionary information; and  
       a decoding unit for decoding said compressed data on the basis of said decompressing dictionary selected by said decompressing dictionary selecting unit.  
     
     
       53. The data decompressing apparatus according to  claim 52 , wherein said decoding unit decodes said compressed data by predetermined character data group on the basis of said decompressing dictionary selected by said decompressing dictionary selecting unit. 
     
     
       54. The data decompressing apparatus according to  claim 53 , wherein if data to be compressed that is said compressed data before compressed is document-form data, said character data group is a desired word in said document-form data. 
     
     
       55. The data decompressing apparatus according to  claim 54 , wherein said decoding unit decodes said compressed data on the basis of category information on said word. 
     
     
       56. The data decompressing apparatus according to  claim 52  further comprising: 
       a decompressing inherent dictionary storing unit for storing a dictionary having character data inherent to data to be compressed that is said compressed data before compressed as characteristic data of said compressed data, in which a predetermined code is assigned to each of said characteristic data as decompressing dictionary;  
       wherein said decoding unit decodes said compressed data on the basis of said decompressing inherent dictionary in said decompressing inherent dictionary storing unit and said decompressing dictionary in said decompressing dictionary storing unit.  
     
     
       57. The data decompressing apparatus according to  claim 56 , wherein said decompressing inherent dictionary storing unit receives information on a compressing inherent dictionary created by extracting character data inherent to said data to be compressed as characteristic data of said data to be compressed and assigning a predetermined code to each of said characteristic data from a compressing side having generated said compressed data to store said decompressing inherent dictionary. 
     
     
       58. The data decompressing apparatus according to  claim 52  further comprising: 
       a decompressing dictionary updating unit for updating said decompressing dictionary on the basis of a result of decoding by said decoding unit;  
       wherein said decoding unit decodes said compressed data on the basis of said decompressing dictionary updated by said decompressing dictionary updating unit.  
     
     
       59. A data decompressing apparatus for decoding compressed data to be decompressed, comprising: 
       a decompressing dictionary storing unit for storing plural different kinds of dictionaries usable to decompress said compressed data;  
       a decompressing dictionary selecting unit for receiving selected dictionary information on a compressing dictionary selected according to a determination of whether a quantity of compressed data is smaller than an original quantity before compressing from a compressing side having generated said compressed data to select a decompressing dictionary to be used among said plural different kinds of decompressing dictionaries on the basis of said received selected dictionary information: and  
       a decoding unit for decoding said compressed data on the basis of said decompressing dictionary selected by said decompressing dictionary selecting unit.  
     
     
       60. The data decompressing apparatus according to  claim 59 , wherein said decoding unit decodes said compressed data by predetermined character data group on the basis of said decompressing dictionary selected by said decompressing dictionary selecting unit. 
     
     
       61. The data decompressing apparatus according to  claim 60 , wherein if data to be compressed that is said compressed data before compressed is document-form data, said character data group is a desired word in said document-form data. 
     
     
       62. The data decompressing apparatus according to  claim 61 , wherein said decoding unit decodes said compressed data on the basis of category information on said word. 
     
     
       63. The data decompressing apparatus according to  claim 59  further comprising: 
       a decompressing inherent dictionary storing unit for storing a dictionary having character data inherent to data to be compressed that is said compressed data before compressed as characteristic data of said compressed data, in which a predetermined code is assigned to each of said characteristic data as decompressing dictionary;  
       wherein said decoding unit decodes said compressed data on the basis of said decompressing inherent dictionary in said decompressing inherent dictionary storing unit and said decompressing dictionary selected by said decompressing dictionary selecting unit.  
     
     
       64. The data decompressing apparatus according to  claim 63 , wherein said decompressing inherent dictionary storing unit receives information on a compressing inherent dictionary created by extracting character data inherent to said data to be compressed as characteristic data of said data to be compressed and assigning a predetermined code to each of said characteristic data from a compressing side having generated said compressed data to store said decompressing inherent dictionary. 
     
     
       65. The data decompressing apparatus according to  claim 59  further comprising: 
       a decompressing dictionary updating unit for updating said decompressing dictionary on the basis of a result of decoding by said decoding unit;  
       wherein said decoding unit decodes said compressed data on the basis of said decompressing dictionary updated by said decompressing dictionary updating unit.  
     
     
       66. A data compressing method for coding inputted data to be compressed, comprising: 
       deciding at a deciding stage whether a compressing dictionary is to be used or not when said inputted data is considered for coding, based on a portion of the inputted data and a portion of the compressing dictionary;  
       coding said inputted data to produce coded data on the basis of said compressing dictionary when it has been decided at said deciding stage that said compressing dictionary is to be used, and outputting the coded data; and  
       outputting the same inputted data without coding when decided at said deciding stage that said compressing dictionary is not to be used for coding.  
     
     
       67. A data compressing method for coding inputted data to be compressed, comprising: 
       selecting a compressing dictionary to be used among plural different kinds of compressing dictionaries on the basis of an extension of a file name of inputted file data to be compressed: and  
       coding said inputted file data on the basis of said selected compressing dictionary.  
     
     
       68. A data compressing method for coding inputted data to be compressed, comprising: 
       selecting a compressing dictionary including high-ranked N character data of high occurrence frequency in said inputted data among plural different kinds of compressing dictionaries; and  
       coding said inputted data to be compressed on the basis of said selected compressing dictionary.  
     
     
       69. A data compressing method for coding inputted data to be compressed, comprising: 
       coding said inputted data and outputting information of a quantity of the coded data;  
       determining whether the quantity of the coded data is smaller than an original quantity before the coding; and  
       selecting a compressing dictionary to be used among plural different kinds of compressing dictionaries according to whether the quantity of the coded data is smaller than the original quantity before the coding.  
     
     
       70. A data decompressing method for decoding inputted data to be decompressed, comprising: 
       receiving dictionary use or non-use information on whether a decompressing dictionary is to be used or not when said inputted data is considered for decoding from a compressing side;  
       deciding whether said decompressing dictionary is to be used according to said received dictionary use or non-use information;  
       decoding said inputted data to produce coded data on the basis of said selected decompressing dictionary when it has been decided that said decompressing dictionary is to be used, and outputting the decoded inputted data; and  
       outputting the same inputted data without decoding when decided said decompressing dictionary is not to be used at said deciding.  
     
     
       71. A data decompressing method for decoding compressed data to be decompressed, comprising: 
       receiving selected dictionary information on a compressing dictionary selected on the basis of an extension of a file name of file data to be compressed from a compressing side having generated compressed file data;  
       selecting a decompressing dictionary to be used among plural different kinds of decompressing dictionaries on the basis of said received selected dictionary information; and  
       decoding said compressed file data on the basis of said selected decompressing dictionary.  
     
     
       72. A data decompressing method for decoding compressed data to decompress the same comprising: 
       receiving selected dictionary information on a compressing dictionary selected as a compressing dictionary including specific character data of high occurrence frequency in data to be compressed from a compressing side having generated said compressed data;  
       selecting a decompressing dictionary to be used among plural different kinds of decompressing dictionaries on the basis of said selected dictionary information received at said receiving; and  
       decoding said compressed data on the basis of said selected decompressing dictionary.  
     
     
       73. A data decompressing method for decoding compressed data to be decompressed, comprising: 
       receiving selected dictionary information on a compressing dictionary selected according to a determination of whether a quantity of compressed data is smaller than an original quantity before compressing from a compressing side having generated said compressed data;  
       selecting a decompressing dictionary to be used among plural different kinds of decompressing dictionaries on the basis of said selected dictionary information received at said receiving; and  
       decoding said compressed data on the basis of said selected decompressing dictionary.  
     
     
       74. A data compressing or decompressing dictionary creating apparatus for creating a dictionary used when data to be compressed is compressed or compressed data is decompressed comprising: 
       a data dividing unit for dividing data for creating a dictionary into predetermined character data groups;  
       an occurrence frequency counting unit for counting an occurrence frequency of each of said character data groups obtained by said data dividing unit;  
       a high occurrence frequency character data group detecting unit for detecting a character data group whose occurrence frequency is higher than predetermined frequency on the basis of said occurrence frequency of each of said character data groups counted by said occurrence frequency counting unit;  
       a code assigning unit for assigning a predetermined code to said high occurrence frequency character group detected by said high occurrence frequency character group; and  
       a dictionary generating unit for combining said high occurrence frequency character group with said code and outputting a combination thereof, thereby generating said dictionary;  
       wherein if said data for creating a dictionary is document-form data, said character group is a desired word in said document-form data, and said code assigning unit adds part-of-speech information of said word to said word. 
     
     
       75. A recording medium readable by a computer in which a data compressing program for coding inputted data to be compressed is recorded characterized in that said data compressing program makes said computer function as: 
       a compressing dictionary storing unit for storing a compressing dictionary usable to compress said inputted data;  
       a compressing dictionary use or non-use deciding unit for deciding whether said compressing dictionary is to be used or not when said inputted data is considered for coding; and  
       a coding unit for coding said inputted data on the basis of said compressing dictionary when said compressing dictionary use or non-use deciding unit decides said compressing dictionary is to be used and outputting the coded data, and outputting the same inputted data without coding when said compressing dictionary use or non-use deciding unit decides said compressing dictionary is not to be used.  
     
     
       76. A recording medium readable by a computer in which a data compressing program for coding inputted data to be compressed is recorded characterized in that said data compressing program makes said computer function as: 
       a compressing dictionary storing unit for storing plural different kinds of compressing dictionaries usable to compress inputted file data to be compressed;  
       a compressing dictionary selecting unit for selecting a compressing dictionary to be used among said plural different kinds of compressing dictionaries on the basis of an extension of a file name of the file data; and  
       a coding unit of coding said inputted file data on the basis of said compressing dictionary selected by said compressing dictionary selecting unit.  
     
     
       77. A recording medium readable by a computer in which a data compressing program for coding inputted data to be compressed is recorded characterized in that said data compressing program makes said computer function as: 
       a compressing dictionary storing unit for storing plural different kinds of compressing dictionaries usable to compress said inputted data;  
       a compressing dictionary selecting unit for selecting a compressing dictionary including high-ranked character data of high occurrence frequency in said inputted data among said plural different kinds of compressing dictionaries; and  
       a coding unit for coding said inputted data on the basis of said compressing dictionary selected by said compressing dictionary selecting unit.  
     
     
       78. A recording medium readable by a computer in which a data compressing program for coding inputted data to be compressed is recorded characterized in that said data compressing program makes said computer function as: 
       a compressing dictionary storing unit for storing plural different kinds of compressing dictionaries usable to compress said inputted data;  
       a coding unit for coding said inputted data using any one of said plural different kinds of compressing dictionaries and outputting quantity information on a quantity of the coded data;  
       a determining unit for determining whether the quantity of the coded data is smaller than an original quantity before the coding based on the quantity information from said coding unit; and  
       a compressing dictionary selecting unit for selecting a compressing dictionary to be used among said plural different kinds of compressing dictionaries according to the determination of said determining unit.  
     
     
       79. A recording medium readable by a computer in which a data decompressing program for decoding inputted data to be decompressed characterized in that said data decompressing program makes said computer function as: 
       a decompressing dictionary storing unit for storing a decompressing dictionary usable to decompress said inputted data;  
       a decompressing dictionary use or non-use deciding unit for deciding whether said decompressing dictionary is to be used or not when said inputted data is considered for decoding; and  
       a decoding unit for decoding said inputted data on the basis of said compressing dictionary when said decompressing dictionary use or non-use deciding unit decided said decompressing dictionary is to be used and outputting the decoded data, and outputting the same inputted data without decoding when said decompressing dictionary use or non-use deciding unit decides said decompressing dictionary is not to be used.  
     
     
       80. A recording medium readable by a computer in which a data decompressing program for decoding compressed data to be decompressed characterized in that said data decompressing program makes said computer function as: 
       a decompressing dictionary storing unit for storing plural different kinds of decompressing dictionaries usable to decompress compressed file data to be decompressed;  
       a decompressing dictionary selecting unit for receiving selected dictionary information on a compressing dictionary selected on the basis of an extension of a file name of the file data from a compressing side having generated said compressed file data to select a decompressing dictionary to be used among said plural different kinds of decompressing dictionaries on the basis of said received selected dictionary information; and  
       a decoding unit for decoding said compressed file data on the basis of said decompressing dictionary selected by said decompressing dictionary selecting unit.  
     
     
       81. A recording medium readable by a computer in which a data decompressing program for decoding compressed data to be decompressed characterized in that said data decompressing program makes said computer function as: 
       a decompressing dictionary storing unit for storing plural different kinds of decompressing dictionaries usable to decompress said compressed data;  
       a decompressing dictionary selecting unit for receiving selected dictionary information on a compressing dictionary selected as a compressing dictionary including high-ranked character data frequently occurring in data to be compressed from a compressing side having generated said compressed data to select a decompressing dictionary to be used among said plural different kinds of decompressing dictionaries on the basis of said received selected dictionary information; and  
       a decoding unit for decoding said compressed data on the basis of said decompressing dictionary selected by said decompressing dictionary selecting unit.  
     
     
       82. A recording medium readable by a computer in which a data decompressing program for decoding compressed data to be decompressed characterized in that said data decompressing program makes said computer function as: 
       a decompressing dictionary storing unit for storing plural different kinds of decompressing dictionaries usable to decompress said compressed data;  
       a decompressing dictionary selecting unit for receiving selected dictionary information on a compressing dictionary selected according to a determination of whether a quantity of compressed data is smaller than an original quantity before compressing from a compressing side having generated said compressed data to select a decompressing dictionary to be used among said plural different kinds of decompressing dictionaries in the basis of said received selected dictionary information; and  
       a decoding unit for decoding said compressed data on the basis of said decompressing dictionary selected by said decompressing dictionary selecting unit.